avfilter/af_adelay: make it possible to delay channels by exact number of samples

doc/filters.texi

@@ -513,6 +513,7 @@ Set list of delays in milliseconds for each channel separated by '|'.
 At least one delay greater than 0 should be provided.
 Unused delays will be silently ignored. If number of given delays is
 smaller than number of channels all remaining channels will not be delayed.
+If you want to delay exact number of samples, append 'S' to number.
 @end table
 
 @subsection Examples
@@ -524,6 +525,13 @@ the second channel (and any other channels that may be present) unchanged.
 @example
 adelay=1500|0|500
 @end example
+
+@item
+Delay second channel by 500 samples, the third channel by 700 samples and leave
+the first channel (and any other channels that may be present) unchanged.
+@example
+adelay=0|500S|700S
+@end example
 @end itemize
 
 @section aecho

libavfilter/af_adelay.c

@@ -138,14 +138,20 @@ static int config_input(AVFilterLink *inlink)
     for (i = 0; i < s->nb_delays; i++) {
         ChanDelay *d = &s->chandelay[i];
         float delay;
+        char type = 0;
+        int ret;
 
         if (!(arg = av_strtok(p, "|", &saveptr)))
             break;
 
         p = NULL;
-        sscanf(arg, "%f", &delay);
 
-        d->delay = delay * inlink->sample_rate / 1000.0;
+        ret = sscanf(arg, "%d%c", &d->delay, &type);
+        if (ret != 2 || type != 'S') {
+            sscanf(arg, "%f", &delay);
+            d->delay = delay * inlink->sample_rate / 1000.0;
+        }
+
         if (d->delay < 0) {
             av_log(ctx, AV_LOG_ERROR, "Delay must be non negative number.\n");
             return AVERROR(EINVAL);